Replication termination in E. coli and B. subtilis

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Ter elements
Bacterial DNA is circular, and so when it is copied in replication, duplication proceeds in 2 directions at 2 self-sufficient replication forks. These forks contain several factors involved in unwinding, and maintaining the separation of the 2 parent strands of DNA, whilst daughter strands are synthesised. This includes a helicase protein to maintain the neat separation of parent strands as well as several other factors. Ter elements are asymmetric patterns of DNA, approximately 23 base pairs long that act as protein binding sites. The binding of specific proteins to these Ter elements provides a trap for the proceeding replication fork, and catches the replication fork as it passes. There are several ter elements responsible for catching each replication fork, however each ter element is specific in action for the fork passing in one direction only. Thus, the ter element responsible for catching the clockwise replication fork will allow the anticlockwise fork to proceed unchecked, until it is stopped by its own anticlockwise facing ter element fork trap.

The purpose of these fork traps is largely speculated, however it is believed they function to prevent over replication, and to stall a faster fork in the case that one side of the replication was proceeding faster than the other side. the presence of several ter sites for each replication fork indicates a sense of redundancy, and is supported by the highly conserved nature of ter sites and their cognate binding capabilities.

Different species of bacteria possess different cognate binding proteins for ter sites. In this article we will examine the TUS protein present in E. coli, and the RTP (replication termination) protein, present in B. subtilis.

E. coli and TUS protein
E. coli posesses the tus protein, which binds ter elements in the DNA.



"B. subtilis" and RTP protein
B Subtilis posesses the RTP protein, which binds ter elements in the bacterial DNA.



